1. Field of the Invention
This invention relates generally to oil and gas well cementing compositions and specifically to polymeric fluid loss additives for such compositions and methods of making the same for controlling fluid loss during cementing operations without retarding the cement.
2. Description of the Prior Art
Cement compositions are used in the oil and gas industry to cement the annular space in the wellbore between the surrounding formation and the pipe or casing. Typically the cement slurry is pumped down the inside of the casing and back up the outside of the casing through the annular space. The amount of water which is used in forming the cement slurry will vary depending upon the type of hydraulic cement selected and the job conditions at hand. The amount of water used can vary over a wide range, depending upon such factors as the required consistency of the slurry and upon the strength requirement for a particular job. Many times, the hydraulic cement must be placed within or next to a porous medium, for example earthern strata in the wellbore. When this happens, water tends to filter out of the slurry and into the strata during placement and setting of the cement. Many difficulties are related to an uncontrolled fluid loss of this type such as an uncontrolled setting rate, improper placement of the slurry, impaired strength properties, and a contamination of the surrounding strata. These conditions are all undesirable in oil and gas well cementing operations.
In order to lessen the fluid loss from the aqueous cement slurry, various materials have been employed in the past. One such material was a copolymer of an acrylamide and acrylic acid. This fluid loss material has the ability to maintain fluid loss control over a wide temperature range, functioned well in the presence of salts, and was superior to cellulose base additives when chloride salt accelerators were present. In spite of these advantages, the copolymer of acrylamide and acrylic acid exhibited latent retarding effects, thereby lessening the usefulness of the material in cement compositions used in low temperature environments.
The object of the present invention is to provide a low fluid loss additive blend for a cement composition which is non-retarding and thus useful in cement compositions at lower temperatures.